How to display the disired gradient effect on TFT LCD

[jerry_coffee]

Hello all,

We hava a proble about display gradient effect, the picture shows as below:

computer display  normal:

imx6ul board display badly（RGB interface） ,the gradient  have ripples on TFT LCD:

our imx6ul board eLCDIF hardware was disigned 24 data line for RBG888 , the DTB configure as below:

&iomuxc {
    myimx6a7-lcd-pad {
		pinctrl_lcd_lcdif_ctrl: lcd_lcdif_ctrl_grp {
  			fsl,pins = <
 				MX6UL_PAD_LCD_CLK__LCDIF_CLK	    0x79
 				MX6UL_PAD_LCD_ENABLE__LCDIF_ENABLE  0x79
 				MX6UL_PAD_LCD_HSYNC__LCDIF_HSYNC    0x79
 				MX6UL_PAD_LCD_VSYNC__LCDIF_VSYNC    0x79
 				MX6UL_PAD_LCD_RESET__GPIO3_IO04		0x79
  			>;
  		};
		pinctrl_lcd_lcdif_data: lcd_lcdif_data_grp {
 			fsl,pins = <
 				MX6UL_PAD_LCD_DATA00__LCDIF_DATA00  0x79
 				MX6UL_PAD_LCD_DATA01__LCDIF_DATA01  0x79
 				MX6UL_PAD_LCD_DATA02__LCDIF_DATA02  0x79
 				MX6UL_PAD_LCD_DATA03__LCDIF_DATA03  0x79
 				MX6UL_PAD_LCD_DATA04__LCDIF_DATA04  0x79
 				MX6UL_PAD_LCD_DATA05__LCDIF_DATA05  0x79
 				MX6UL_PAD_LCD_DATA06__LCDIF_DATA06  0x79
 				MX6UL_PAD_LCD_DATA07__LCDIF_DATA07  0x79
 				MX6UL_PAD_LCD_DATA08__LCDIF_DATA08  0x79
 				MX6UL_PAD_LCD_DATA09__LCDIF_DATA09  0x79
 				MX6UL_PAD_LCD_DATA10__LCDIF_DATA10  0x79
 				MX6UL_PAD_LCD_DATA11__LCDIF_DATA11  0x79
 				MX6UL_PAD_LCD_DATA12__LCDIF_DATA12  0x79
 				MX6UL_PAD_LCD_DATA13__LCDIF_DATA13  0x79
 				MX6UL_PAD_LCD_DATA14__LCDIF_DATA14  0x79
 				MX6UL_PAD_LCD_DATA15__LCDIF_DATA15  0x79
 				MX6UL_PAD_LCD_DATA16__LCDIF_DATA16  0x79
 				MX6UL_PAD_LCD_DATA17__LCDIF_DATA17  0x79
 				MX6UL_PAD_LCD_DATA18__LCDIF_DATA18  0x79
 				MX6UL_PAD_LCD_DATA19__LCDIF_DATA19  0x79
 				MX6UL_PAD_LCD_DATA20__LCDIF_DATA20  0x79
 				MX6UL_PAD_LCD_DATA21__LCDIF_DATA21  0x79
 				MX6UL_PAD_LCD_DATA22__LCDIF_DATA22  0x79
 				MX6UL_PAD_LCD_DATA23__LCDIF_DATA23  0x79
 			>;
 		};
    };
};

&lcdif {
    pinctrl-names = "default";
    pinctrl-0 = <&pinctrl_lcd_lcdif_ctrl 
            &pinctrl_lcd_lcdif_data>;
    display = <&display0>;
    status = "okay";

    display0: display {
        bits-per-pixel = <32>;
        bus-width = <24>;
	 
        display-timings {
        native-mode = <&timing0>;
            timing0: timing0 {
                clock-frequency = <51000000>;
                hactive = <1024>;
                vactive = <600>;
                hfront-porch = <250>;
                hback-porch = <160>;
                hsync-len = <70>;
                vback-porch = <25>;
                vfront-porch = <12>;
                vsync-len = <12>;

                hsync-active = <0>;
                vsync-active = <0>;
                de-active = <1>;
                pixelclk-active = <1>;
            };
        };
    };
};

The eLCDIF driver path: drivers/video/fbdev/mxsfb.c

what can i do for it?  thanks

[Ahmet_Cihan_AKINCA]

I've the same problem with my imx7d-based custom board. I think it's not about timings or hardware pins, I've checked all of things for days.. it's an graphics processing issue, an software issue. However I couldn't solve my problem although I tried 3 different kernels. My 24-bit parallel LCD and Ti's tsc2004 touchscreen working fine except for that gradient trouble!

[joanxie]

the display timgings depends on your lcd date sheet, you can double check it, and did you add "if=RGB24,bpp=16" or "if=RGB24,bpp=24" in your uboot?

[jerry_coffee]

thanks the reply~

LCD displaying pictures is perfect, besides image that has gradients.

using fbset  cmd to get informations about LCD configs in Kernel

mode "1024x600-52"
# 51.002 MHz, H: 33.911 kHz, V: 52.251 Hz
geometry 1024 600 1024 600 32
timings 19607 160 250 25 12 70 12
accel false
rgba 8/16,8/8,8/0,0/0
endmode

I have tried to set dpp:16, dpp:24  and 32, gradients displays not good on LCD-TFT.

witch one to decides the display effect of gradients?

any options tell to me, thanks.

[joanxie]

what tft panel do you use? did you double confirm if your timings settings according to your display data sheet?

[jerry_coffee]

Yes, i have calculated timing parameters according to datasheet support by vendor.

this is our lcd reference manual parts of timing setting.

display-timings {
        native-mode = <&timing0>;
            timing0: timing0 {
                clock-frequency = <51000000>;
                hactive = <1024>;
                vactive = <600>;
                hfront-porch = <250>;
                hback-porch = <160>;
                hsync-len = <70>;
                vback-porch = <25>;
                vfront-porch = <12>;
                vsync-len = <12>;

                hsync-active = <0>;
                vsync-active = <0>;
                de-active = <1>;
                pixelclk-active = <1>;
            };
        };

any you needed i will support if i can.

Looking forward to you reply.

thanks.

[joanxie]

 hfront-porch = <250>;
                hback-porch = <160>;
                hsync-len = <70>;

why did you get hfront-porch=250? refer to the data sheet, it should be 160, and where did you get hback-porch?